Peet's is really different from Caribou because Peet's really shines on great tasting espresso and steamed milk in their beverages. You're getting less "candy in a cup" (where flavor syrups or toppings mask the taste of espresso), and more "coffee"...which is what this corporate chain is famous for.
My favorite drink at the moment is a soy cappuccino made with 1 pump of maple. The iced matcha latte with coconut, raspberry or peppermint is fantastic and their herbal Xiao's Blend tea is delciously refreshing hot or iced. If you're looking for Caribou favorites, they have a toasted marshmallow mocha and they can still make the white chocolate peppermint mocha as well.
If you're a fan of hot coffee, Blend 101 is my favorite so far. They also have a "Pick of the Month" which is a featured coffee that they have limited stock on. Each Pick of the Month is special and vary in their characteristics. So far, my favorite POM was Ethiopia Queen City around late July/August.